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Harrow (tool)
]] ]] , commonly used to compact soil after it has been loosened by a harrow]] , Australia]] )]] In agriculture, a harrow (often called a set of harrows in a plurale tantum sense) is an implement for breaking up and smoothing out the surface of the soil. In this way it is distinct in its effect from the plough, which is used for deeper tillage. Harrowing is often carried out on fields to follow the rough finish left by ploughing operations. The purpose of this harrowing is generally to break up clods (lumps of soil) and to provide a finer finish, a good tilth or soil structure that is suitable for seedbed use. Such coarser harrowing may also be used to remove weeds and to cover seed after sowing. Harrows differ from cultivators in that they disturb the whole surface of the soil, such as to prepare a seedbed, instead of disturbing only narrow trails that skirt crop rows (to kill weeds). There are four general types of harrows: disc harrow, tine harrow, chain harrow and chain disk harrows. Harrows were originally drawn by draft animals, such as horses, mules, or oxen, or in some times and places by manual labourers. In modern practice they are almost always tractor-mounted implements, either trailed after the tractor via a drawbar or mounted on the three-point hitch. Types In cooler climates the most common types are the disc harrow, the chain harrow, the tine harrow or spike harrow and the spring tine harrow. Chain harrows are often used for lighter work such as levelling the tilth or covering seed, while disc harrows are typically used for heavy work, such as following ploughing to break up the sod. In addition, there are various types of power harrow, in which the cultivators are power-driven from the tractor rather than depending on its forward motion. Tine harrows are used to refine seed-bed condition before planting, to remove small weeds in growing crops and to loosen the inter-row soils to allow for water to soak into the subsoil. The fourth is a chain disk harrow. Disk attached to chains are pulled at an angle over the ground. These harrows move rapidly across the surface. The chain and disk rotate to stay clean while breaking up the top surface to about deep. A smooth seedbed is prepared for planting with one pass. Chain harrowing may be used on pasture land to spread out dung, and to break up dead material (thatch) in the sward, and similarly in sports-ground maintenance a light chain harrowing is often used to level off the ground after heavy use, to remove and smooth out boot marks and indentations. When used on tilled land in combination with the other two types, chain harrowing rolls the remaining larger clumps of soil to the surface where the weather will break them down and prevent interference with seed germination. All four harrow types can be used in one pass to prepare the soil for seeding. It is also common to use any combination of two harrows for a variety of tilling processes. Where harrowing provides a very fine tilth, or the soil is very light so that it might easily be wind-blown, a roller is often added as the last of the set. Harrows may be of several types and weights, depending on the intended purpose. They almost always consist of a rigid frame to which are attached discs, teeth, linked chains or other means of cultivation, but tine and chain harrows are often only supported by a rigid towing-bar at the front of the set. In the southern hemisphere the so-called giant discs are a specialised kind of disc harrows that can stand in for a plough in very rough country where a mouldboard plough will not handle the tree-stumps and rocks, and a disc-plough is too slow (because of its limited number of discs). Giant scalloped-edged discs operate in a set, or frame, that is often weighted with concrete or steel blocks to improve penetration of the cutting edges. This sort of cultivation is normally immediately followed by broadcast fertilisation and seeding, rather than drilled or row seeding. A drag is a heavy harrow. Historical reference In Europe, harrows were first used in the early Middle Ages. The following text is taken from the Household Cyclopedia of 1881: "When employed to reduce a strong obdurate soil, not more than two harrows should be yoked together, because they are apt to ride and tumble upon each other, and thus impede the work, and execute it imperfectly. On rough soils, harrows ought to be driven as fast as the horses can walk; because their effect is in the direct proportion to the degree of velocity with which they are driven. In ordinary cases, and in every case where harrowing is meant for covering the seed, three harrows are the best yoke, because they fill up the ground more effectually and leave fewer vacancies, than when a smaller number is employed. The harrowman's attention, at the seed process, should be constantly directed to prevent these implements from riding upon each other, and to keep them clear of every impediment from stones, lumps of earth, or clods, and quickens or grass roots; for any of these prevents the implement from working with perfection, and causes a mark or trail upon the surface, always unpleasing to the eye, and generally detrimental to the vegetation of the seed. Harrowing is usually given in different directions, first in length, then across, and finally in length as at first. Careful husbandmen study, in the finishing part of the process, to have the harrows drawn in a straight line, without suffering the horses to go in a zigzag manner, and are also attentive that the horses enter fairly upon the ridge, without making a curve at the outset. In some instances, an excess of harrowing has been found very prejudicial to the succeeding crop; but it is always necessary to give so much as to break the furrow, and level the surface, otherwise the operation is imperfectly performed." George Orwell,George Orwell, 1952, Homage to Catalonia, Harcourt & Brace, ISBN 0-15-642117-8 (Harvest pbk.), p 80 as a soldier in 1937 in a Spanish Civil War anti-fascist unit three miles east of Huesca, Aragon, found inside “a derelict hut in no man’s land” a harrow of primitive design: "There was a kind of harrow that took one straight back to the later Stone Age. It was made of boards joined together, to about the size of a kitchen table; in the boards hundreds of holes were morticed, and into each hole was jammed a piece of flint which had been chipped into shape exactly as men used to chip them ten thousand years ago." See also * List of agricultural machinery * Roller (agricultural tool) * Harrower (surname) References External links *"Degelman Strawmaster Harrows" Tine Harrows *"Little Harrows" Song parody *"Martens Harrows" Spike harrows *"Pepin Harrows" Spike & Coil Tine Harrows *"May-Bridge Harrows" Chain harrows *Examples of harrows Category:Agricultural machinery Category:Tillage